Metals and Non-metalsPhysical Properties
The easiest way to start grouping substances is to compare how they look and behave — their physical properties. A school lab would hand you samples of iron, copper, aluminium, magnesium, sodium, lead and zinc. Our virtual bench has five of them, and a set of simple tools.
Metals
Activities 3.1 to 3.4 and 3.6 all happen on this one bench. Rub each sample with sandpaper and look at its surface, try a sharp knife on it, strike it with a hammer, try to draw it into a wire, put it in a circuit with a bulb, and drop it on a hard floor. Every result is written into Table 3.1.
Complete both missions. Pick a sample, then run the tests on it.
Your table shows six properties of metals. Here is each one with its proper name.
- Metallic lustre. A metal in its pure state has a shining surface. An old sample looks dull only because of a coating that forms in air; sandpaper rubs it off.
- Hardness. Metals are generally hard, but the hardness varies from metal to metal — sodium is soft enough to cut with a knife.
- Malleability. Many metals can be beaten into thin sheets. Gold and silver are the most malleable metals; that is how the silver warq on a barfi is made.
- Ductility. Metals can be drawn into thin wires. Gold is the most ductile metal: a wire about 2 km long can be drawn from just one gram of gold.
- Electrical conductivity. Metals let an electric current pass through them, which is why the bulb glowed.
- Sonority. Metals that produce a ringing sound when they strike a hard surface are called sonorous. That is why school bells are made of metal.
Malleability and ductility let us give metals any shape we need: sheets for cooker bodies, wires for the electricity in your home. And those wires always wear a coat of PVC or rubber. Why?
Right. Metals conduct, so a bare live wire would pass current into your hand. PVC and rubber do not conduct, so they keep the current inside the wire.
Why Pans Are Made of Metal
Which metals does your kitchen use for cooking vessels — and why those? Activity 3.5 finds out. An aluminium or copper wire is clamped to a stand, and a pin is fixed to its free end with a drop of wax. Then the wire is heated with a spirit lamp near the clamp.
Predict: what will you see after some time?
The heat travelled all the way along the wire and melted the wax at the far end, yet the wire itself did not melt. So metals are good conductors of heat and have high melting points — exactly what a cooking vessel needs. The best conductors of heat are silver and copper, which is why many steel pans are given a copper bottom. Lead and mercury are comparatively poor conductors of heat.
Non-metals
There are far fewer non-metals than metals. Carbon, sulphur, iodine, oxygen and hydrogen are some of them. Non-metals are either solids or gases — except bromine, which is a liquid.
Do non-metals share the physical properties of metals? Activity 3.7 runs the same tests on them. Collect carbon (as coal, and as graphite — the "lead" of your pencil), sulphur and iodine, and fill in their rows of Table 3.1.
Complete all three missions.
Compare the two tables. Non-metals are mostly dull and brittle — they crumble instead of flattening — they cannot be drawn into wires, they do not ring, and they do not conduct electricity. Almost the opposite of metals. Almost.
Rules with Exceptions
You found two rebels yourself. There are more, and together they show that we cannot group elements by their physical properties alone.
(i) All metals are solids at room temperature except
(ii)
(iii) Carbon is a non-metal that can exist in different forms; each form is called an allotrope. Diamond, one allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point. Graphite, another allotrope, is a
(iv) The alkali metals — lithium, sodium and potassium — are so
Too many exceptions. Elements are sorted far more clearly by their chemical properties — starting with what happens to their oxides.
The Litmus Verdict
Activity 3.8 burns one metal and one non-metal and asks their oxides a question. A magnesium ribbon burns with a dazzling white flame and leaves a white ash, which is dissolved in water. Sulphur powder burns with a blue flame; a test tube held over it collects the fumes, and a little water is shaken up inside. Both solutions are tested with red and blue litmus paper.
Magnesium's ash, dissolved in water: what does it do to litmus?
Magnesium oxide is basic:
And the solution of sulphur's fumes?
Sulphur dioxide is acidic:
This is a much clearer test. Most metals give basic oxides; most non-metals give acidic oxides. In the next section you will meet metal oxides in more detail.
Speed Round: Metal or Non-metal?
Every clue below describes a real element, and several of them are the rule-breakers you have just met. Read the clue, then decide.
Get five right to move on.